This application claims Paris Convention priority of DE 100 15 788.2 filed Mar. 30, 2000 the entire disclosure of which is hereby incorporated by reference.
The invention concerns a device for examining the sterility of fluids, in particular pharmaceutical products, comprising a diaphragm filter for sterile filtering of the fluid, which is inserted into a filtering unit, a collecting container for the filtered matter, which can be connected to an outlet of the filtering unit, and a container receiving at least one nutrition medium to incubate the diaphragm filter for detecting microorganisms.
To examine the sterility of fluids which have to meet the highest hygienic standards, e.g. liquid, emulsified or dissolved pharmaceutical substances, active substances or the like and other filterable products, the fluid is usually filtered by means of a diaphragm filter which is impermeable to microorganisms and the diaphragm filter is subsequently incubated in a nutrition medium which, in case of microbial contamination of the fluid, produces an increase in the microorganisms accumulating on the filter. The propagation of microorganisms can be monitored and documented permanently or at regular time intervals thereby permitting qualitative detection of the microbial contamination of the test medium. The diaphragm filter is optionally washed before incubation in the nutrition medium to exclude any errors in the determined bacterial count caused by different fluid matrices, e.g. fluids having different antibiotic and consequently bacterial growth-blocking effects. The diaphragm filter must have a pore width of less than 0.45 xcexcm in accordance with the required guidelines, e.g. the current pharmacopoeias, to guarantee retainment of the microorganisms on the filter. A similar approach is used in water technology for determining the bacterial count of water, e.g. drinking water, tap water, ground water, surface water, waste water or the like and in food technology.
Devices for sterile filtering of fluids are known which comprise a filtering unit which can be mounted onto a collecting container for the filtered matter and into which a diaphragm filter can be inserted which is usually designed as an annular disc. The fluid is supplied to the diaphragm filter by applying an underpressure to the collecting container which is designed e.g. like a suction bottle or by applying an overpressure on a reservoir connected to the filtering unit and accommodating the fluid to be examined. After sterile filtering, the diaphragm filter is manually transferred into a container having the nutrition medium, e.g. via a pair of tweezers, the container is closed and incubated at a predetermined temperature for a predetermined time. The replication of the microorganisms retained on the filter, which occurs in case of microbial contamination of the fluid, is usually visually assessed by the cloudiness of the medium accompanying bacterial growth. Disadvantageously, the complicated handling of the diaphragm filter does not permit automatic examination of a plurality of samples, and the free handling of the diaphragm filter, in particular during transfer of the filtering unit into the nutrition medium, risks contamination from the surroundings which can lead to erroneous positive results.
Moreover, closed devices comprising several filtering units, each accommodating one diaphragm filter, and a pump connected therewith are known. The fluid to be examined, an optional wash solution, and the nutrition solution are successively supplied to the diaphragm filters by means of the pump. When the filtering units are filled with the nutrition solution, thereby wetting the diaphragm filter, the filtering units are closed, removed from the device and incubated to assess bacterial growth in case of microbial contamination of the fluid. Although this largely prevents subsequent contamination of the diaphragm filter, the device is demanding and expensive.
It is the underlying purpose of the invention to further develop a device of the initially mentioned type in a simple and inexpensive fashion such that reproducible results are obtained and erroneous positive results are reliably prevented.
In accordance with the invention, this object is achieved in a device of the initially mentioned type in that the diaphragm filter can be inserted into and removed from the filtering unit by a handling device and be moved without contact into the container containing the nutrition medium by the same handling device.
The inventive handling device largely prevents contact between the diaphragm filter and the surroundings, in particular when removing the diaphragm filter from the filtering unit and moving same into the nutrition solution, thereby reliably preventing external contamination of the diaphragm filter which would lead to erroneous positive results. The inventive device permits a substantially sterile transfer of the diaphragm filter into the container holding the nutrition medium. The container may be advantageously designed as a measuring unit for automatic detection of microbial growth, which is particularly advantageous with large numbers of samples. Such automatic detection of the microorganism growth, e.g. through continuous or regular measurement of its metabolic products, such as carbon dioxide, eliminates the conventional visual assessment of the medium which requires substantial time and personnel. The device can be universally applied for different sample volumes and pore sizes of the diaphragm filter. The handling device is preferably integrated in the diaphragm filter.
In a preferred embodiment, the handling device comprises a cap with a filler neck for the fluid to be filtered, the wash solution, or the like, which can be mounted on the filtering unit and also on the container receiving the nutrition medium. In this fashion, the diaphragm filter can be removed from the filtering unit after sterile filtration of the fluid to be examined and optional washing, and be disposed on the container receiving the nutrition medium for incubation, thereby wetting the diaphragm filter with the nutrition medium. To seal the container receiving the nutrition medium with the diaphragm filter during incubation, the filler neck of the cap can be tightly sealed e.g. by means of a stopper.
In a preferred embodiment, a screw connection is provided between the handling device of the diaphragm filter and the filtering unit as well as on the container receiving the nutrition medium in order to provide a sealing connection between the handling device receiving the diaphragm filter and the filtering unit or the container accommodating the nutrition medium, which can be easily closed and opened.
The connection between the diaphragm filter and the handling device is preferably a releasable connection e.g. a plug connection or a weakened region, in particular a breaking point which can preferably be manually released by means of an actuator disposed on the handling device. A handling device of this type which is integrated in the diaphragm filter and connected therewith via a releasable connection, e.g. a breaking point, guarantees fundamental sterility, wherein the entire unit may be sealed, in particular by the manufacturer, to preclude external contamination of the diaphragm filter. In this fashion, the cap of the handling device can be removed from the filtering unit after sterile filtering and optional washing of the filter and the diaphragm filter can be removed from the filtering unit by means of the handling device connected therewith and disposed onto the container receiving the nutrition medium for incubation. Manual triggering of the actuator of the handling device releases same from the diaphragm filter along the breaking point causing the diaphragm filter to fall into the nutrition solution of the incubation container to be rinsed by the nutrition solution on its inner and outer side. Subsequently, the container may be closed and incubated by means of a lid integrated e.g. in the handling device.
The diaphragm filter is preferably either substantially cylindrical or substantially slightly conical or truncated and connected to the handling device at an open end face, wherein the connection between the diaphragm filter and the handling device can preferably be released, as mentioned above, and designed e.g. as a breaking point or plug connection. A diaphragm filter designed in this fashion has a considerably larger surface for retaining and collecting microorganisms from the sample medium compared to that of conventional diaphragm filters, designed as annular discs, which, in the subsequent test, permits an improved flow of microorganisms through the nutrition medium and therefore improved measuring accuracy and reproducibility, while thereby preventing erroneous positive results.
To prevent back-flow of the filtered matter from the collecting container (which is usually not sterile) into the coupled filtering unit and thereby contamination of the diaphragm filter, a preferred embodiment provides for disposition of a retaining means for the filtered matter in the collecting container in the region of the outlet of the filtering unit and/or in the region of an intake of the collecting container, which can be connected therewith. The retaining means may be formed e.g. like a bacteria-tight filter, in particular a diaphragm filter or a valve, such as a check valve.
Preferably, a plug connection, e.g. a nozzle is provided between the filtering unit and the collecting container, wherein e.g. the filtering unit comprises, at its lower side, a centering projection, surrounding the outlet, for mounting to a holding projection formed on the upper side of the collecting container or on a lid of same. This ensures that the outlet of the filtering unit tightly abuts an intake disposed at the upper side of the collecting container or on its lid when the filtering unit is mounted on the collecting container.
The device in accordance with the invention is furthermore preferably autoclavable.
The invention is described in more detail below by means of a preferred embodiment and with reference to the drawing.